# Mitigating the Rock‐Salt Phase Transformation in Disordered LNMO Through Synergetic Solid‐State AlF3/LiF Modifications

## TL;DR

This paper introduces a method to improve the performance of a lithium-ion battery cathode material by preventing structural changes that limit its lifespan.

## Contribution

A synergistic solid-state modification with LiF and AlF3 is proposed to mitigate rock-salt phase transformation in LiNi0.5Mn1.5O4.

## Key findings

- The dual modification with LiF and AlF3 enables near-complete delithiation/lithiation and enhances structural stability.
- The optimized material retains 80% of its capacity after 200 cycles at 0.5C with high cathode loading.
- High reversible capacities are achieved at various current rates, up to 142.1 mAh·g⁻¹ at 0.2C.

## Abstract

High‐voltage disordered spinel LiNi0.5Mn1.5O4 is a promising cathode material for high power density in lithium‐ion batteries. However, it suffers from poor cycle life associated with the rock‐salt phase transformation. This study presents a straightforward synthesis approach to enhance the electrochemical performance of LiNi0.5Mn1.5O4 through a synergistic solid‐state modification with LiF and AlF3. This dual modification promotes rapid Li⁺ diffusion, enables near‐complete delithiation/lithiation, approaching the theoretical capacity of disordered LiNi0.5Mn1.5O4, and, more importantly, effectively mitigates the formation of the rock‐salt phase, thereby enhancing structural stability, as confirmed by operando X‐ray absorption spectroscopy (XAS) and synchrotron X‐ray diffraction (SXRD). As a result, the optimized LiNi0.5Mn1.5O4 (10 mg AlF3 + 30 mg LiF) delivers high reversible capacities of 142.1, 139.1, 129.2, 121.6, 110.3, 93.5, and 76.1 mAh∙g−1 at 0.2C, 0.5C, 1.0C, 2.0C, 3.0C, 4.0C, and 5.0C, respectively. Full cells using graphite as the anode and a high‐loading cathode exhibit excellent cycling performance. They retain 80% of their capacity after 200 cycles at 0.5C within a voltage window of 3.5–4.9 V with cathode loading of 11 mg∙cm−2. The findings of this study will significantly advance high‐power LiNi0.5Mn1.5O4 materials, offering improved battery life and thereby enhancing their potential for practical applications.

The transition between the spinel and rock‐salt phases induces irreversible structural changes in disordered LiNi0.5Mn1.5O4, thereby preventing it from fully releasing its electrochemical capacity during charge/discharge cycling.